The field of the invention relates to plastic foams, and more particularly, to relatively rigid polyurethane foams which are to be laiminated to a polyester resin formed from the reaction of an unsaturated polyester laiminating resin which contains an unsaturated monomer such as styrene. One process for forming such a lamination is disclosed in an application by Francis Gallap and the present inventor in U.S. Pat. No. 3,859,401 filed on Aug. 9, 1971 which patent is hereby incorporated by reference herein.
Many useful articles can be made from a laminate having an outer skin of a polyester resin such as fiberglass-reinforced polyester resin and an inner layer of a rigid polyurethane foam. Such laminates have been widely used in the construction of boats. While various processes have been used to form such laminates, a problem common to all prior art processes is poor adhesion at the interface between the polyester layer and the foam.
While the process disclosed in the above-described U.S. Pat. No. 3,859,401 leads to substantially improved adhesion, still further improvements would permit a further increase in load-bearing ability and thus could permit wider use of such panels as, for instance, in multi-story buildings fabricated from polyester-polyurethane laminates.
For example, a panel made according to the process disclosed in the above-identified U.S. Pat. No. 3,859,401 was tested according to ASTM E-72-68 (12) which is an impact test wherein a 60 pound bag is dropped on one face of a panel which is supported on two rollers which are separated by a 7 foot span. The initial drop is made from 6 inches and if the panel does not fail, the bag is dropped from increasing heights, which increase is at the rate of 6 inches per drop. A 2-inch thick panel having a skin thickness of 1/16th of an inch made according to the process disclosed in the above-identified application failed at 18 inches whereas a panel having the same dimensions made according to the present invention did not fail until the bag was dropped at a height of 7 feet.
Loading tests were run on 4 ft. .times. 8 ft. panels having a 2 inch overall thickness and two outer skins of 1/16th inch thickness. The load was applied along the 4 foot edge and the test was carried out according to ASTM E-72-68 (7). Panels made according to the process of the above-identified application withstood a load of about 600 pounds per lineal foot before laterally deflecting 1/20 of their length. Panels having the same dimensions made according to the process disclosed in the present application reached this same deflection level with a load of about 1,200 pounds per lineal foot.
Various other approaches have been tried to improve the adhesion between fiberglass-reinforced polyester and rigid polyurethane foam. These processes include the addition of a fiberglass chop which partially protrudes from one surface of a cured polyester sheet. A polyurethane pre-foam is then spread over the surface and is held to the polyester sheet by a physical entanglement and entrapment resulting from the foaming of the polyurethane in and around the extending glass fibers. While such a process provides some bonding, it does not result in a complete bond of the surface but merely relies upon an entrapment which occurs only at the points where glass fibers protrude from the surface. Another approach is to first form a cured polyurethane rigid foam followed by the planing of the surface of the foam to remove the shiny outer skin of the polyurethane. The resin and fiberglass may then be laid upon the surface of the planed foam which can result in a satisfactory bond. Such a process, however, requires several additional steps not necessary with the practice of the present invention. Still another process involves the provision of a barrier layer between the fiberglass-polyester and the polyurethane, which layer is capable of adhering both to the polyester and to the polyurethane. Such a process not only requires an additional step but also introduces a potential layer of weakness not present with the practice of the present invention.